The present invention relates to a broadband switching network for megahertz frequency signals of the type described in the periodical Nachrichten der Telefonbau & Normalzeit (1980) Heft 82, "TN-Fernsprechsystem 6030 Zeitmultiplex mit farbtuchtigem elektronischen Video-Koppelfeld" [TN-Nachrichten Telefonbau und Normalzeit (1980), No. 82, "TN 6030 time-division multiplex system with color-compatible electronic video matrix panel], by Bruno Beuss, Peter Loewenhoff, Bernhard Rall, Rudolf Saumweber.
The switching network described therein connects together forty video telephone subscribers by means of semiconductor crosspoints. For this purpose, use is made of a triangular switching network which has one crosspoint for each connection but is provided with two switches, one for each one of the two transmission directions for the video telephone signals to be transmitted between two subscribers. The subscribers are connected through the crosspoint in a manner which is unbalanced with respect to ground.
Monolithically integrated crosspoint arrays having 5.times.2 crosspoints, each composed of two switches, are used for this purpose. For better decoupling, such semiconductor modules are assembled in a forty-pin ceramic package having a copper shield on all sides. For the same reasons, all lines carrying video signals are enclosed by shielding or control lines. All of these lines are accommodated in a multilayer printed circuit board.
The above-described broadband switching network is operated at frequencies up to 10 megahertz.
There exists a need for a switching network capable of handling even higher frequencies because of the ever increasing shortage of frequencies for cable television systems in which, for example, 30 television channels must be distributed to individual subscribers in such a manner that each subscriber can receive a number of these channels. In addition, care must be taken, under certain circumstances, to allow different subscribers to receive different combinations of channels. Distribution is then preferably effected in that carrier frequency range in which television receivers handle broadcast signal reception, as discussed in the article in Wissenschaftliche Berichte AEG-Telefunken [Scientific Reports from AEG-Telefunken], Vol. 53 (1980) 1-2, at pages 62-71.